1. Field of Invention
This invention relates to the electrophysiological catheter electrode band used in the mapping (measurement of electrical potential), pacing (stimulation of the muscle tissue by pulsing an electrical current), and ablating (burning the tissue by use of high electrical current) of the heart's inner wall. This invention generally relates to catheters and leads used in sensing electrical activity within a patient and administering therapy, and more particular to such catheter and leads incorporating band electrode configured for flexibility and tractability within the body.
2. Discussion of Related Art
A method of construction of a conductive band electrode is typically now accomplished by using a rigid thin wall, metal tube (example: platinum/iridium alloy, stainless steel) band which is swaged or adhesively bonded in place and over where a conductor wire is tied onto the catheter's flexible polymer (example: PVC, polyurethane) hollow tube. This method of construction has some technical and design drawbacks. Some of these are:
1. Rigid metal bans limit catheter flexibility and make the ability of the catheter to reach a desired area impossible.
2. Rigid metal bands cannot be long in length. More than one centimeter can effect the flexibility and curve radius of the catheter, thus preventing the electrode from being placed where required.
3. Rigid metal bands have the possibility of sliding off the catheter and being lost inside the patient.
4. Pressure of the catheter flexible polymer tube and the inside wall of the band typically loosely attach the rigid metal bands to the conductor wire. Catheter flexing can then cause intermittence in the electrical signals.
5. Rigid metal bands are on the surface of the catheter's polymer tube and have corner edges which are exposed to the patient's tissue. This can cause trauma due to abrasions.
6. Rigid metal bands can also allow fluid leakage under and into the space between the band and the catheter's polymer tube. This can cause loss of signal and sterility issues.
7. Rigid metal band configuration (number and length of bands) and spacing between bands is also a problem. By trying to place bands less the one millimeter apart, difficulties are experienced in the manufacturing and performance of the catheter.
Another method of band design construction was conceived as an improvement over rigid metal bands using conductive adhesives bands (adhesives filled with a metal or other conductive powder used as the electrical conductor). This colloidal suspension matrix is flexible and thus allows for longer bands and better placement of the catheter's electrodes onto the required tissue wall; but it also has some design weaknesses:
1. The randomly dispersed conductor particles depend on a continuous touching (but not joined) to allow for the conductance of electrical current. These abutting connections can easily be broken by the curving and flexing of the catheter's polymer tube over which the conductive adhesive is applied. The resulting problems are intermittent signal and spark gap across the conductive particles.
2. Another potential problem is the loss of conductive particles into the patient's blood stream. If the adhesive bond of a band's conductive particle located at the outer surface is weak, the electrical energies conducted through the band's matrix could cause the breaking of the polymer adhesive's and conductive particle's bond and therefore liberate the particle into the patient's body.
3. Manufacturing issues are presented, such as the control of accuracy of the band's placement, the uniformity of the band's thickness, and control of the chemical science which relates to the polymer's adhesive and cohesive properties between not only the conductive particles and adhesive polymer, but also the adhesive polymer and the catheter's polymer tube.
4. Electrical current distribution could also be random and difficult to control because of the varied powder's distribution pattern throughout the inner wall, middle sections and onto the outer surface of the conductive adhesive bands.
A variation on the rigid metal band electrode is the slotted metal band electrode. The advantage of the slotted metal band is derived from several slots that are placed in a pattern around and throughout a metal band to allow flexibility. Basically this concept is still a rigid metal band and therefore many of the problems which occur in rigid metal bands still occur in the slotted metal bands, or are sometime compounded due to the slots. For example, a band's corner edges, which could cause tissue abrasions, in traditional non-slotted rigid metal bands number only two (a leading and a tailing corner edge). This problem has been increased with the slotted metal bands because of its multiple possible abraiding corners. The slots also may harbor foreign matter if not thoroughly cleaned.
Unique to the prior band construction methods is a continuously wound metal wire spring coil which is wrapped around or molded into the outer surface of the catheter's distal tip and connected by a wire to transmit an electrical signal to function as an electrode. This method of band construction also gives flexibility but suffers from the need for special tooling and a higher degree of manufacturing process control. The joints between the coil loops may also harbor foreign matter if not thoroughly cleaned.
The last method compared is called thin film electrodes, which is a thin metal film that is deposited by means of vapor deposition onto the completed assembled catheter's distal tip. This metal band is flexible, but the nature of the material is such that, over time, flexing of the metal will cause stress cracks leading to band to failure. This method has some difficulties in its manufacturing process, e.g. it requires a high degree of technology and the catheter's distal tip must be completely assembled prior to the thin film application.
The above concepts have been mentioned in an attempt to give a clear contrast to the subject invention of the composite flexible conductive bands.
It also should be noted that there has been no attempt to describe the well-established process of cardiac catheter construction, so as not to distract from the focus of the invention and concept of the composite flexible and conductive band.